The measurement of fluid flow through a centrifugal pump with convenient read-out of repeatable accuracy has generally been a difficult process and typically requires the attachment of sensors and instrumentation downstream of the pump. At the same time, there is a demand for a simple, effective and reliable means for measuring fluid flow at the pump itself. A typical centrifugal pump of the prior art comprises an impeller rotatably mounted in a stationary casing, with the rotating impeller imparting pressure and kinetic energy to the fluid being pumped, with the stationary casing guiding the fluid to and from the impeller. In a typical centrifugal pump casing, which generally includes concentric, diffusor and volute type centrifugal casings, the rotation of the impeller imparts kinetic energy to the fluid and causes fluid flow, in a generally circular direction about the perimeter of the impeller, through the casing surrounding the impeller. At some point in the casing, the fluid flows from the perimeter of the impeller, passes a cut-water or the like, flows through an area of the pump generally known as the discharge inlet area and flows through the discharge nozzle to the pump discharge outlet.
In the operation of the pump, the fluid flow can be affected by the design of the impeller, the design and size of the casing, the speed at which the impeller rotates, the design and size of the pump inlet and outlet, quality of finish of the components, presence of a casing volute and the like. The incorporation of flow measurement devices within the pump are typically seen as creating added obstruction to fluid flow and further flow variations.
U.S. Pat. No. 5,129,264, Centrifugal Pump with Flow Measurement, discloses an improved pump casing and process for measuring fluid flow through a centrifugal pump casing wherein the static pressure of a fluid being pumped by the pump is measured at a first point in the pump discharge inlet area of the pump adjacent the flow arm of the pump and at a second point removed along the nozzle, the measured pressures are compared to a pre-determined flow constant of the casing. However, in some pump designs the nozzles or other hydraulic passage areas do not diverge enough to give a measurable differential pressure reading.
The principal object of this invention is to provide a centrifugal pump adapted for measuring fluid flow where the internal area changes are not great enough to provide meaningful flow measurements, thereby eliminating the need for a separate flow measuring device. This and other objects of the invention will become apparent from the following.